Inner tie rod for securing wall forms

ABSTRACT

An inner tie rod has an anti-rotation offset of a configuration providing a minimum tendency to weaken the rod, while retaining all the necessary resistance to rotation.

United States Patent [191 [111 3,830,461 Williams Aug. 20, 1974 1 INNER TIE ROD FOR SECURING WALL 3,160,988 12/1964 Williams 249 213 O MS 3,405,904 10/1968 Williams 3,667,720 6/1972 Williams 249/213 [76] Inventor: Chester I. Williams, 1501 Madison v SE, Grand Rapids, Mich. 49507 Primary Examiner-Richard .1. Herbst [22] 1972 Attorney, Agent, or Firm-Glenn B. Morse [21] Appl. No.: 302,490

52 us. Cl. 249/213, 249/42 1 1 ABSTRACT 51 l t. Cl. E04 17 E04 1 8 of Search n 2 g /2 0 5 29 An inner tie rod has an anti-rotation offset of a config- 2 uration providing a minimum tendency to weaken the rod, while retaining all the necessary resistance to ro- [56] References Cited tauon' UNITED STATES PATENTS 4 Claims, 3 Drawing Figures 3,013,323 12/1961 Williams 249/217 h... W45! raw/l INNER TIE ROD FOR SECURING WALL FORMS BACKGROUND OF THE INVENTION The construction of concrete walls normally involves pouring liquid concrete in the space between parallel form panels held in predetermined relationship by a pattern of tie systems. Each of these includes a central tie rod extending perpendicularly to the panels across a major part of the intervening space. Bolts normally traverse both of the panels, and are in threaded engagement with the opposite ends of the tie rod, Bridging members or bearing brackets transfer the loading on the bolts to beams stiffening or supporting the form panels, with the net result at the pressure from the poured concrete is balanced out through the inner tie rod. After the concrete sets, the bolts are unscrewed, leaving the inner tie rod embedded in set concrete.

It has been recognized as desirable to provide a solid interlock between the inner tie rod and the set concrete for two purposes. One of these is to prevent sufficient separation to invite the ingress of moisture, and the other is to provide sufficient resistance to rotation so that the bolts can be unscrewed without the necessity of using complicated arrangements for operation on both ends the inner tie rod at the same time for application of opposite torque. The usual means for providing the interlock between the inner tie rod and the surrounding concrete is to provide either a set of forged lateral extensions or a central offset in the tie rod. The present invention is associated with the latter arrangement, the former being less practical as the use of severely cold-worked material for the inner tie rod becomes common. The strength of the tie rod material is only useful up to the yield point, since any attempt to use the ultimate strength of the rod as a design determinant would necessarily involve a sufficient extension of the rod as to remove all accuracy of placement of the forms. Economical utilization of the tie rod material therefore dictates that it be cold-worked to the point that yield stress approaches as closely as is practical to the ultimate stress of the material. Cold-working to this degree has the unfortunate tendency to render the material somewhat brittle, and to invite the formation of cracks when ever sharp deviations from the initial straight rod stock are attempted to be used.

When attempts are made to minimize the extent of the lateral offset of the central tie rod, another problem immediately emerges. An offset of gentle curvature to reduce the cracking tendency, and of a limited degree of offset, produces a corresponding tendency for the entire rod to turn within the concrete in the manner of a flexible shaft inside its housing. It must be kept in mind that at the time at which the tie bolts are disengaged from the inner tie rod is usually such that the concrete cannot be considered fully cured. The strength of this concrete is therefore very limited, and a high-tensile steel rod with a gentle degree of offset configuration is easily capable of twisting its way loose in such concrete. Experiments have established, however, that an offset configuration relates to the diameter of the rod stock can be established which will provide satisfactory retension with the concrete without seriously weakening the rod, and without increasing the risk of failure resulting from crack formation in the manufacture of the rod.

SUMMARY OF THE INVENTION An offset configuration is provided by this invention which will provide the necessary retension under most conditions with a single offset preferably in the middle of the length of the rod. This offset has an arcuate central portion having an inside radius of curvature between 4 and 6 times the diameter of the rod, and preferably 4% times the rod diameter. The lateral extent of the offset is in an amount between three-sixteenths and five-sixteenths the diameter of the rod, and preferably one-fourth of the rod diameter. This central arcuate portion of the offset is preferably joined to the rod on the opposite sides of the offset by curved portions having a radius of curvature opposite to that of the central offset, and of an inside amount at least equal to the rod diameter.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary section of a portion of a wallforrn system at one of the tie assemblies.

FIG. 2 is a side elevation on an enlarged scale showing the inner tie rod incorporated in the FIG. 1 assembly.

FIG. 3 is a diagram showing the configuration of the central offset of the tie rod.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the form panels 10 and 11 are stiffened, respectively, by the vertical studs 12 and 13. These studs are spaced along the horizontal extent of the panels as may be required by a stress analysis covering the form installation. At appropriate vertically spaced positions, pairs of waler beams l4lS and 16-17 are used to transfer the loading from the studs to the illustrated tie system. Bolts as shown at 18 and 19 traverse the form panels 10 and 11, and also the spacing between the walers. These bolts are in threaded engagement with'the opposite ends of the inner tie rod 20. Conventional wedges 21 and 22 are normally interengaged with broached flats on the opposite sides of the bolts, and bridge across the walers to transfer the stresses at this point. So-called hairpin spacers are frequently used, and have one leg traversing a suitable hole in the bolts to function as a transverse pin bearing against the inside of the walers to establish a spacing of the forms by cooperating with the wedges to positively establish the position of the walers with respect to the bolts.

The central tie rod 20 has threaded opposite ends 25- and 26, which normally are interengaged with the interior threading in the conical ends 27 and 28 at the inner extremities of the bolts 18 and 19. The tie rod 20 has a central offset 29 designed to establish a resistance to rotation with respect to the surrounding concrete after it has at least partially set. The configuration of the central offset 29 is shown diagrammatically in FIG. 3. The central arcuate portion of the offset 29 is determined by the inside arc 30 and the outside arc 31. Experiments have established that the most effective range for the inside are 30 is between 4 and 6 times the diameter of the rod 20, and preferably 4% times this diameter. A radius of curvature in this amount can be imparted to the rod, even in the cold-worked state without serious risk of generating cracks. A radius of curvature in excess of that specified in the above range has a tendency to induce the problem referred to previously as analogous to the functioning of a flexible shaft within its housing. A radius of curvature less then that specified produces a danger of generating cracks and local surface deformity that invites stress concentration. It is obvious that the exterior radius 31 will be greater then the interior radius 30 by the amount of the rod diameter.

\ To make effective use of the specified range of the radii of curvature, the amount of the offset indicated at 32 in FIG. 3 should be within the range of threesixteenths and five-sixteenths of the rod diameter. This extent of offset appears to interact favorably with the specified range of radii of curvature to produce the necessary results, the preferred amount of the offset being one-fourth of the rod diameter. These ratios of radii of curvatureand offset with respect to rod diameters appear to hold'within the usual range of rod diameters used with this type of form-securing system. This range extends from a nominal rod diameter of 0.27 2 to 1.146 inches.'It is intended for severely cold-worked steel rods in which the yield point is 80 percent or more of the ultimate strength of the rod stock.

While it is theoretically possible to determine the point of intersection of the radius 30 with the projection of the side of the rod 20, and specify distance between these points as indicated at 33 in FIG. 3, it must be recognized that these points are of merely academic interest. It is impossible to form the rod with a sharp transition from the acuate portion to the straight portions on either side of it, and it would be undesirable to do this in view of the tendency to invite cracks and stress consentration at these points. With this in mind, it is preferable to to provide arcuate transition portions of opposite curvature to the central arcuate: portion, and interconnecting this central portion to the straight portions of the rod (or to an adjacent opposite offset) with a smooth pattern free of abrupt deviations. The.

inside transition radii 34 and 35 are shown in FIG. 3 to be substantially the same as the inside radius 30, with the corresponding junction radii 36 and 37 being similar to the radius 31. The radii 34 and 35 do not appear to be necessarily limited to a one-for-one relationship with the radius 30, and can be decreased to an amount equal to the diameter of the rod 20, with corresponding decrease in the radii 36 and 37. The possibility of such decrease is probably due to the fact that the reversal of curvature between the central and the transition curvature produces opposite stresses in adjacent portions of the material of the rod 20 which thus tends to be mutually relieving against the tendency to form surface cracks. In the FIG. 3 diagram, the diameter of the rod is indicated at 38, and the rod radius (or half of the diameter) at 39. The theoretical amounts of the offset to the centers of the radii of the curvature, indicated at 40 and 41 (or at 42, as an alternative) are normally of layout interest only, as it is easier to specify and check the extent of the offset in terms of the dimension shown at 32, with the radius of curvature normally being checked by appropriate templets.

I claim:

1. In combination with a wall form tie system, an inner tie rod having threaded opposite ends and at least one central offset for inhibiting rotation in concrete wherein the improvement comprises:

a configuration of said offset having the following characteristics:

a. an arcuate central portion having an inside radius of curvature of between four and six times the diameter of said rod; and

b. a lateral extent of said offset in an amount between three sixteenths and five sixteenths of the diameter of said rod.

2. A combination as defined in claim 1, wherein said central portion is joined to the portions of said rod on the opposite sides of said offset by arcuate portions of curvature opposite to that of said central portion, and of an inside amount at least equal to said rod diameter.

3. A combination as defined in claim 1, wherein said radius of curvature is substantially four and one-half times said rod diameter.

4. A combination as defined in claim 1, wherein said offset is substantially one quarter of said rod diameter. 

1. In combination with a wall form tie system, an inner tie rod having threaded opposite ends and at least one central offset for inhibiting rotation in concrete wherein the improvement comprises: a configuration of said offset having the following characteristics: a. an arcuate central portion having an inside radius of curvature of between four and six times the diameter of said rod; and b. a lateral extent of said offset in an amount between three sixteenths and five sixteenths of the diameter of said rod.
 2. A combination as defined in claim 1, wherein said central portion is joined to the portions of said rod on the opposite sides of said offset by arcuate portions of curvature opposite to that of said central portion, and of an inside amount at least equal to said rod diameter.
 3. A combination as defined in claim 1, wherein said radius of curvature is substantially four and one-half times said rod diameter.
 4. A combination as defined in claim 1, wherein said offset is substantially one quarter of said rod diameter. 